Inhibition of cellobiohydrolases from Trichoderma reesei. Synthesis and evaluation of some glucose-, cellobiose-, and cellotriose-derived hydroximolactams and imidazoles

The lactam 16, the hydroximolactams 8, 20, 23, and 27, and the imidazole 32 were prepared following known methods. They were tested together with the known tetrazole 35 and the hydroximolactams 2 and 36 as inhibitors of the c ellobiohydrolases Cel7A and Cel6A from Trichoderma reesei. Cel7A is only we akly inhibited by these compounds. Comparing their inhibitory activity evid ences the importance of occupying subsites tl and +2. We results strongly s uggest that the shape of none of the variants of the lactone-type inhibitor motif embodied by these inhibitors is complementary to the subsite - 1, i. e.,analogous to the transition state. Cel6A is rather strongly inhibited by the cellobiose analogues 20, 23, and 32, and by the cellotriose analogue 2 7. Their relative inhibitory activities evidence that binding at subsite -2 depends upon the shape of the moiety occupying subsite - 1. There is only a small difference between the inhibition by the hydroximolactams 20 and 23 , which may be (partially) protonated by the catalytic acid of either anti- or syn-protonating glycosidases, and the imidazole 32, which can only be p rotonated by anti-protonating glycosidases. The results strongly suggest th at shape requirements must be met by glycosidase inhibitors before they can be used to characterize the proton trajectory of glycosidases.